odd pushrod behavior

[Ardenfour]

got my md1 back together after skimming the faces so I have to make quite a large adjustment to the valve clearances (the valves were 'dropped' according to the engineering co.) the valve end of the two rockers now sit angled upwards, whereas before they sat horizontal. I had to adjust them by about 5mm to close the clearance gap. is this a problem?
what is odd, the exhaust pushrod seems 'springy' - I adjust the clearance of the rocker, but I can press the pushrod end down about 3mm and it springs back up, as if there's a spring below the tappet.
any thoughts please?

 

[rogerboy]

could be oil in the follower, but you will be doing the tappets again after it has been run, after you have built up give a full turn by hand before starting,

 

[TQA]

got my md1 back together after skimming the faces so I have to make quite a large adjustment to the valve clearances (the valves were 'dropped' according to the engineering co.) the valve end of the two rockers now sit angled upwards, whereas before they sat horizontal. I had to adjust them by about 5mm to close the clearance gap. is this a problem?
what is odd, the exhaust pushrod seems 'springy' - I adjust the clearance of the rocker, but I can press the pushrod end down about 3mm and it springs back up, as if there's a spring below the tappet.
any thoughts please?

None of this sounds 'right' to me. Did you have the valves refaced and the seats reground?

I would investigate further before trying to start it. At the very least turn it by hand through two full revoltions.

 

[lenseman]

got my md1 back together after skimming the faces . . . . . . the valve end of the two rockers now sit angled upwards, whereas before they sat horizontal. . . . . . .

Something very wrong with the set up and the way you have described the current rocker angle?? If you have had a large amount skimmed off the face of the head and or block, and 5mm is an extreme amount, the rockers (at the valve end), should be angled downwards not upwards!



.

 

[cimo]

the valves were 'dropped' according to the engineering co.

not sure what dropped means. (looking to be educated here)

but I can press the pushrod end down about 3mm and it springs back up, as if there's a spring below the tappet.
any thoughts please?

tappet should sit firm on the camshaft lobe, push rod firm in the tappet. You got some debris in the tappet bucket or something binding between the tappet & its guide? 5mm adjustment sounds way out.

Are these new rods (i.e. correct lenght)?

 

[Marsupial]

got my md1 back together after skimming the faces so I have to make quite a large adjustment to the valve clearances (the valves were 'dropped' according to the engineering co.) the valve end of the two rockers now sit angled upwards, whereas before they sat horizontal. I had to adjust them by about 5mm to close the clearance gap. is this a problem?
what is odd, the exhaust pushrod seems 'springy' - I adjust the clearance of the rocker, but I can press the pushrod end down about 3mm and it springs back up, as if there's a spring below the tappet.
any thoughts please?

There are lots of things going on here that are not correct, without seeing it its difficult to be precise but for starters:

The valves were "dropped" I take this to mean they had pulled into the head, a common problem. To correct this the head should be counter bored and new seats fitted, its a standard procedure. It sounds like they just re-cut the seats compounding the problem. The valves are now even deeper in the head.

The "Angle of the rocker is now wrong", well if the seat is too deep and they took a large skim off the head - more than (25 thou is excessive) then this would be the case. It could also be that the valve stems are too long - wrong valves fitted perhaps. Don't forget they take metal from the head face and valve seat but the push rod stays the same length so the geometry is compromised, but 5mm is excessive.

"Push rods are springy", this needs further investigation but it could be that the valve stems are too long (for the reasons mentioned above) and the valve springs are standard length so there would be or could be a lack of valve spring compression to "hold the valve train together". OR it could be that the push rods are bent, OR the tappets are missing; either way its not right needs more investigation and I would be wary of starting the engine.

Prepare yourself for a new cylinder head if they have skimmed too much off because that error is irretrievable.

 

[Ardenfour]

thanks for responses. the engine starts and runs OK, given that the bump clearance setup may be a bit hit-or-miss (cardboard for shims) both head and block were skimmed, but nowhere near 5mm. it seems as though the valve stems are now too long.

 

[Bosun Higgs]

I agree with the others. Something wrong here. No way should you have to adjust the rockers by 5mm. The max likely of 20 thou off head and block ( and why would he need that much) is only 1mm so where did the other 4 come from?

Did he replace the valves themselves? Is there an assembly error? I would not want to run or rely on that engine til I knew the answer.

 

[Lakesailor]

There are lots of things going on here that are not correct, without seeing it its difficult to be precise but for starters:

The valves were "dropped" I take this to mean they had pulled into the head, a common problem. To correct this the head should be counter bored and new seats fitted, its a standard procedure. It sounds like they just re-cut the seats compounding the problem. The valves are now even deeper in the head.


The "Angle of the rocker is now wrong", well if the seat is too deep and they took a large skim off the head - more than (25 thou is excessive) then this would be the case. It could also be that the valve stems are too long - wrong valves fitted perhaps. Don't forget they take metal from the head face and valve seat but the push rod stays the same length so the geometry is compromised, but 5mm is excessive.


"Push rods are springy",

The two highlighted points I agree with.

Springy push rods. I've come across that before. I can't remember what I did to solve it - not very helpful, I know.

 

[Marsupial]

I agree with the others. Something wrong here. No way should you have to adjust the rockers by 5mm. The max likely of 20 thou off head and block ( and why would he need that much) is only 1mm so where did the other 4 come from?

Did he replace the valves themselves? Is there an assembly error? I would not want to run or rely on that engine til I knew the answer.

5mm is big difference but dont forget that rockers are not symetrical so a small difference on pushrod side because of all the engineering work and the fact that the push rod length has not changed will magnify on the valve clearance side - draw it you will see what I mean; but 5mm is still way out. There is more to this than we know, without seeing and measuring it is difficult to understand what has transpired.

 

[Jcorstorphine]

I had pushrods bend on a Volvo MD2B. 5 mm is an huge gap when skimming the head is only about 0.5mm or less, Just does not seem right.

 

[Ardenfour]

Ok, here's a picture inlet valve closed. Notice the angle of the rocker. The thread showing above the adjuster locknut is the amount I had to unscrew to close the valve. At the top of the valve, the rocker bears on the edge of the valve stem rather than on the flat. I agree something seems amiss, I can't work out what. Engine fired up right away and seems to run ok through the revs, bit lumpy but hard to tell, the thing jumps all over the place.
Damn, can't upload from phone, will do it tonight

 

[Lakesailor]

I seem to think that the springy pushrod I came across before (not on a marine engine) was cured with replacement pushrods. Take the push rods out and roll them on a flat surface (with cup and bottom end clear of the flat plane). Are they straight? Is the machined bottom end OK? Is the tappet a free fit in it's hole? Does the "springiness" still occur straight after the engine has run?

 

[Ardenfour]

Difficult to describe, but the springiness is not in the pushrod, rather as if there was a small spring under the tappet. I can press it down against resistance, then it hits something solid. It springs back up when released.

 

[Ardenfour]

Further, it's almost like air is trapped under the tappet, though I would have thought running the engine would have cleared this

 

[Lakesailor]

That's what I was trying to suggest but thought someone would cleverly point out it isn't a hydraulic tappet.

 

[scottie]

Don't like the idea of cardboards shims under the block piston clearance is critical i suspect cardboard will squeeze out if wet!

Water in the block resulting in bent push rods is quite common in these engines along with brocken valve springs.

 

[lenseman]

. . . . quite common in these engines along with brocken valve springs.

Ahh, in a situation like this, it would be the Brocken Spectre



.

 

[Marsupial]

Ok, here's a picture inlet valve closed. Notice the angle of the rocker. The thread showing above the adjuster locknut is the amount I had to unscrew to close the valve. At the top of the valve, the rocker bears on the edge of the valve stem rather than on the flat. I agree something seems amiss, I can't work out what. Engine fired up right away and seems to run ok through the revs, bit lumpy but hard to tell, the thing jumps all over the place.
Damn, can't upload from phone, will do it tonight

OK so have you put the inlet rocker on the exhaust valve and vis versa. OR have you swapped the rocker shaft carriers over so they are now offset? The rocker should bear slightly to one side of the valve stem so the valve turns as it goes up and down.

It could be running like a dog because the pistons are now hitting the head - it doesn't sound good

 

[Jcorstorphine]

None of this adds up.

If the head and the block were skimmed and nothing else changed, then the tappet clearance would be less as the height of the centre line of the rocker shaft relative to the centre line of the camshaft would now be less then before.

In addition, if the valve seats had been reground, then the top of the valve stem would now be higher than before relative to the rocker shaft thus making the pushrod end of the rocker down further towards the camshaft again making the clearance less.

I assume that you have used genuine Volvo or Keypart shim gaskets which are not too compressible.

Have you also checked the piston height to the block with a clock gauge. This should be done with the block pulled down using spacers so that the tie rods can be bolted down so as to compress the shim gasket.

Lastly, when I rebuilt my MD2B from the crankshaft up, I am sure I used some lead wire inserted into the injector port so that I could compress it with the piston and then measure the flattened wire with a micrometre to check the final "bump clearance"